how far can his missiles reach out of syria? is he likely -- i mean, should other nations in the area be concerned? >> well, i think by definition this is very dangerous stuff, and it's unstable, mads obviously to being highly toxic. it's dangerous for anybody to be around. one of the problems with chemical weapons has always been how you deliver them. the explosive force of normal ar tillery or missile destroys the chemical weapons. being able to actually use it effectively has been a military problem. i don't think that it's likely assad would use this across the turnish border, for example. i think it's far more likely he's threatening the opposition and basically either for negotiating purposes or because he thinks he's close to the end of the line, he's making it clear he's getting ready to use his ultimate weapon to increase his leverage. >> greta: i did some research on sarin gas. this is what happened in the minute. runny nose, tightness in chest, constriction of pupils. difficulty breathing, nausea, vomiting, defecating